Question

I have done some tests with QueryPerformanceCounter and got strange results.
It seems that my simple program refreshes slowly (about 40ms) when it doing nothing, but when I put RedrawWindow with RDW_INVALIDATE message it refreshes and works very fast (about 1ms)

Please look at the examples:

{…}

double PCFreq = 0.0;
__int64 now = 0, start = 0;

LARGE_INTEGER li;

PCFreq = double(li.QuadPart)/1000;

AllocConsole( );  
freopen("CONOUT$", "wb", stdout);

double delay;

while (GetMessage (&messages, NULL, 0, 0))
{
        QueryPerformanceCounter(&li);    
        now = li.QuadPart;

        if ( double(now - start) / PCFreq >= 40)
        {
                **// painting !!!**

         cout <<  double(now - start) / PCFreq << "\n";
         start = now;
        }

        // !!!!!!
        **RedrawWindow(hwnd, NULL, NULL, RDW_VALIDATE);** 

        TranslateMessage(&messages);
        DispatchMessage(&messages);

    }

    FreeConsole( );   

{…}

When the RedrawWindow(hwnd, NULL, NULL, RDW_VALIDATE); is in main loop I can obtain exacly 40ms or even 5ms, but without RedrawWindow(hwnd, NULL, NULL, RDW_VALIDATE); the condition if ( double(now – start) / PCFreq >= 40) is entering no faster than 45-50 ms….

My question is:
How can I avoid RedrawWindow(hwnd, NULL, NULL, RDW_VALIDATE); function but keep fast refreshing. When Iam using RedrawWindow(hwnd, NULL, NULL, RDW_VALIDATE); my interface (buttons, windows) not displays.

THANKS!

Answer 1

GetMessage does not return unless there is a message in the message queue. By calling RedrawWindow, you are putting a Message in the queue every single iteration of the loop. Use PeekMessage instead of GetMessage:

while (true)
{
    if (PeekMessage(&messages, NULL, 0, 0, PM_REMOVE))
    {
        if (messages.message == WM_QUIT)
            break;
        TranslateMessage(&messages);
        DispatchMessage(&messages);
    }

    // Do your stuff here
}